shared subnet declaration behavior between 2 pools

Bob Harold rharolde at umich.edu
Mon Oct 9 20:25:02 UTC 2017


On Mon, Oct 9, 2017 at 4:10 PM, project722 <project722 at gmail.com> wrote:

> Hello. im curious as to how dhcpd determines what pool to pull a lease
> from in a shared subnet declaration. for ex on our server we have:
>
> shared-network "Market 1" {
>         option domain-name "example.com";
>                 subnet 192.168.1.0 netmask 255.255.255.0 {
>                 option broadcast-address 192.168.1.255;
>                 option routers 192.168.1.1;
>                 pool {
>
>
>                        failover peer "dhcp-failover";
>                        range 192.168.1.10 192.168.1.254;
>
>         }
>         subnet 192.168.2.0 netmask 255.255.255.0 {
>                 option broadcast-address 192.168.2.255;
>                 option routers 192.168.2.1;
>                 pool {
>
>                         failover peer "dhcp-failover";
>                         range 192.168.2.10 192.168.2.254;
>
>
>                }
> }
>
> I would suspect that the broadcasts that come through these
> routers/gateways determine the pool that dhcp assigns a lease from. So, if
> a client requests is seen by the sever comes from 192.168.1.1 it will get a
> lease out of that pool, and if it sees that the client requests cvomes from
> 192.168.2.1 it will get a lease from that pool. Is my understanding correct
> on this? If that is correct, then what happens when the 192.168.1.0 network
> gets full? Does dhcpd have some type of algo that allows it to assign a
> lease from the 192.168.2.0 pool in order to prevent an out of leases
> condition?
>
>
What I have observed is that DHCPD tends to fill the first pool, regardless
of which router forwarded the request.  When the first pool, gets full, it
starts using the second.  Once all have been used, it reuses the 'oldest'
entry (LRU - least recently used).

-- 
Bob Harold
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